Metal or metal oxide particles of submicron size are a valuable industrial commodity finding use in many applications including for example in the manufacture of industrial catalyst such as might be employed in the chemical industry, in the manufacture of ceramics, of electronic components, and as fillers for, for example, plastics, paints or cosmetics.
A large variety of techniques are available for the manufacture of metal or metal oxide powders having a very fine particle size. Such techniques include solution processes and high temperature gas phase and condensed phase syntheses. For a comprehensive review of the general techniques available reference is made to the recent publication entitled "Chemical Engineering Aspects of Advanced Ceramic Materials" by V. Hlavacek and J. A. Puszynski published in the Journal of Industrial Engineering and Chemical Research, pages 349-377, Volume 35, 1996.
Despite the numerous procedures available, a problem in common to a lesser or greater extent with nearly all methods is the difficulty of obtaining consistently fine uniform particles of good purity. Procedures that can provide a greater consistency in this respect invariably have high costs associated with their operation due to the complexity of the equipment required, the use of expensive and potentially hazardous raw materials, or high energy consumption. Recently two closely related procedures have been published which provide a means of manufacturing submicron sized metal powders without need of complex and costly equipment. In the publication EP-A-621,234 to manufacture metal powders it is required to calcine a polyurethane polymer containing a metal salt; however yields are relatively low. In another publication, WO96/29280 this polyurethane approach has been modified by avoidance of the use of polyisocyanate, a hazardous chemical, with the requirement to subject to calcination a gel or liquid. Gels are difficult to handle or manipulate in such a calcining procedure; handling of solids is highly preferred.
It would therefore be desirable to develop a cost effective procedure leading to the production of metal or metal oxide powders having a consistently fine particle size. It would be of particular advantage if such a procedure could be operated using raw materials readily available and could be operated in the substantial absence of highly specialized equipment and costly solvents or chemical processing aids. It would also be an advantage if such a procedure were able to provide for the production of metal powders in a more attractive yield by calcination of solids in contrast to gels which are notoriously difficult to handle in industrial procedures.